The class of polymers of carbon monoxide and olefin(s) has been known for a number of years. Brubaker, U.S. Pat. No. 2,495,286 produced such polymers in the presence of free radical catalysts, i.e., peroxy compounds. U.K. No. 1,081,304 produced similar polymers of higher carbon monoxide content in the presence of alkylphosphine complexes of palladium salts as catalyst. Nozaki extended this process through the use of arylphosphine complexes of palladium salts and certain inert solvents, e.g., U.S. Pat. No. 3,694,412.
More recently the class of linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon, e.g., ethylene or ethylene and propylene, has become of greater interest, in part because of the greater availability of these polymers. The polymers have been shown to be of the formula --CO(A)-- where A is the moiety of the unsaturated hydrocarbon polymerized through the ethylenic unsaturation. For example, when the ethylenically unsaturated hydrocarbon is ethylene, the polymer is represented by the formula --CO(--CH.sub.2 --CH.sub.2 --. The general process for the production of such polymers is illustrated by a number of published European Patent Applications including No. 0,121,965 and No. 0,181,014. The process generally involves a catalyst composition formed from a compound of the Group VIII metals palladium, cobalt or nickel, the anion of a non-hydrohalogenic acid having a pKa below 2 and a bidentate ligand of phosphorus, arsenic or antimony.
The bidentate ligands are generally of the formula ##STR1## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R are organic groups and M independently is a member of Group VA of the Periodic Table of Elements selected from phosphorus, arsenic and antimony. The process of polymer production is operable with ligands containing a variety of combinations of M atoms, which combinations may call for the two M atoms to be the same or alternatively to be different. Although general preference is given to bidentate ligands of the above formula wherein both M atoms are phosphorus, it has been found than when "mixed" bidentate ligands are employed, i.e., a ligand of differing M atoms is used, one particular combination of M atoms provided results which are improved over other combinations of mixed M atoms and even improved over combinations where both M atoms are the same but are other than phosphorus.